Digital camera devices have continued to increase in complexity and capabilities with the advent of new image capture modes that offer the user unique output image characteristics. One such image capture mode is a composite burst image capture mode where a plurality of images are acquired over a specified time interval and one or more subjects in the scene are extracted from multiple images and combined onto a common background. The resulting composite image provides a stop action effect for the subject in motion as illustrated in FIG. 1A. As a creative mode, this capability enables the user to observe the motion of a skier, the running of a child or any other conditions where subject motion allows for a proper stop-action effect.
A key consideration of the composite burst image mode is the proper selection of the time separation between individual captures that are combined into the single composite image. Currently, for typical embodiments of this image capture mode, various image capture settings (e.g., the number of “burst” images and, either the total time duration for the image sequence or the time spacing between sequential image captures) must be specified via a user interface prior to the user capturing the moment of action. This requires the user to make a guess about the appropriate image capture settings prior to initiating the capture of the sequence of images. Given that knowledge about the motion of the moving objects will be rarely known in advance, this can lead to unsatisfactory results in many cases. This can be further complicated by the fact that the user may forget to adjust the image capture settings before the capture of new conditions. An example of an unsatisfactory result would correspond to the subject moving too slowly relative to the capture rate, resulting in too little separation between the object positions in the resulting composite image as illustrated in FIG. 1B. An analogous problem would occur when the subject is moving too rapidly relative to the capture rate so that it moves too quickly through the camera's field of view. Both of these examples would result in a poor user experience of the resulting output composite image.
Some recently introduced digital cameras include a capability to automatically analyze captured images to determine the motion characteristics present within the image content of interest. The motion characteristics are used for purposes such as determining the optimal exposure time.
Various methods of estimating motion are available to those skilled in the art, the most common of which is to capture two images separated in time and measure the change in spatial location of objects between frames. One such method is described by De Haan in U.S. Pat. No. 5,929,919, entitled “Motion-compensated field rate conversion.”
U.S. Patent Application Publication 2007/0237514 to Pillman et al., entitled “Varying camera self-determination based on subject motion,” teaches a method for capturing digital images where motion in the scene is measured prior to image capture. Various camera settings are adjusted responsive to the determined scene motion.
Capturing a rapid burst of digital images requires a means to buffer the captured image data. Managing a limited amount of memory in a digital camera can present some challenging problems. U.S. Pat. No. 5,016,107 to Sasson et al., entitled “Electronic still camera utilizing image compression and digital storage” teaches a digital camera including a multi-frame image buffer for storage of a burst of digital images. As each digital image is captured, the next available buffer area is loaded and image compression begins. When the image buffer is filled, a control processor interrupts the exposure section so that no further images are captured until an image buffer area is freed.
U.S. Pat. No. 6,885,395 to Rabbani et al., entitled “Selectively adjusting the resolution levels or the quality levels of digital images stored in a digital camera memory,” discloses a digital camera where the resolution level or quality level of stored digital images is adjusted based on the available memory space in the digital camera memory so that a subsequent captured digital image can be stored.
U.S. Pat. No. 6,539,169 to Tsubaki et al., entitled “Method and apparatus for recording and re-recording image data in a device having limited memory capacity,” discloses a digital camera having a limited memory capacity. Digital images are initially recorded a predetermined resolution or compression rate. An image file is then read from the memory and re-recorded after a resolution conversion operation or a re-compression operation is carried out on the digital image data.
There remains a need for a method to adjust image capture settings for an electronic image capture device in a burst image capture mode.